Automotive cruise control automatically controls actual automotive vehicle speed to a target speed, such as may be set by a vehicle operator. Such cruise control may influence engine inlet air or fuel in parallel with other control activities, such as standard engine control activities. Typical engine control applications include a throttle follower mechanism, also commonly referred to as a dashpot mechanism, to improve engine inlet air control performance by damping change in engine intake manifold pressure under certain transient engine operating conditions. The damping is commonly provided through control of an engine intake air bypass valve, such as an idle air control valve, in proportion to the operator-commanded intake air (throttle) valve position. The throttle follower mechanism is typically only active for certain small intake air (throttle) valve openings and, when active, increases the engine intake air gain for a given change in throttle position. The increase in engine intake air gain reduces control stability, and transitions into and out of the limited range of activation of the throttle follower can produce significant engine control perturbations that may be perceptible to the vehicle operator, and that may reflect poorly on engine or vehicle stability.
Furthermore, in parallel cruise control systems in which a cruise control actuator provides for engine intake air valve position variation in parallel to position variation by an accelerator means, such as an accelerator pedal, an amount of cruise control actuator travel may be provided below the throttle valve fully closed position. The amount of cruise control travel below the throttle valve fully closed position is commonly referred to as the cruise control mechanical lash, which must be taken up before the cruise control actuator can impact throttle valve position. For cruise control maneuvers starting from a fully released (or nearly fully released) cruise control actuator position, the time required to take up the mechanical lash can result in increased vehicle speed error and in reduced cruise control responsiveness.
Still further, during severe engine speed or vehicle speed reduction periods characterized by engine control operation in the generally understood deceleration fuel cutoff mode, if cruise control is active and the engine is within an operating range associated with a high sensitivity to fuel command changes, entry into or exit from the deceleration fuel cutoff mode of operation can result in significant and undesirable engine output torque disturbances, which may reflect negatively on engine or vehicle stability.
It would therefore be desirable to provide an improved integration of the parallel functions of cruise control, general engine control, throttle follower control and deceleration fuel cutoff control.